Insurance, finance, and Travel can make much more money. One insurance site could make 50usd a day with just less than 100 visitors.
You can follow popular Europe news sites to find out hot niches in Europe. e.g: Telegraph.co.uk, BBC.co.uk, Dailymail.co.uk, etc.
For AdSense, Mesothelioma. It was one (maybe still is) the highest paying keyword on Google and paid out a ridiculous amount per click. The legend of the multi-dollar payout still abounds, so many people still make sites for it.
Basically niche means that topic on which you blogging.The high paying niche in Adsense are those which widely search and deal with daily human problems. Health Make Money Online Technology Celebrities Fashion Insurance, etc. People prefer to use internet to find tips and solution of many problems and due to which these high paying niche are among the most popular.